Frank a



May 8, 1923. 1,454,442

F. A. HOWARD SPARK PLUG Original Filed April 11 1919 WITNESS INVENTOR.

Patented May 8, 1923.

UNITED STAT lAShMf.

FRANK A. HOWARD, OF STJVISSVALE BOROUGH, PENNSYLVANIA.

Application filed April 11, 1919, Serial No. 2%,403.

To all whom it may concern,-

lle it known that I, FRANK A. Howinu), a citizen of the United States, and residing in the borough of Swissvale. in the county of Allegheny and State of Pennsylvania, have invented or discovered new and useful linprc-vements in Spark Plugs, of which the following is a specification.

My invention consists in certain new and useful improvements in spark plugs used for ignition purposes in connection with internal combustion engines.

More particularly, my spark plug is of that type wherein a visible spark is produced Which indicates whether or not the cylinder is firing properly.

The object which I have in view is the provision of a spark plug of this type which will be inexpensive to manufacture, easy to repair and efficient in operation.

Generally speaking, my improved spark plug is of the following construction. The insulator is made of heat-resisting glass, or other suitable transparent material, and is mounted in the bushing which is attached to the engine cylinder, the bushing being provided with the negative electrode, while the positive electrode is embedded in the material of the insulator when the latter is pressed or molded. The outer end of the insulator is provided with a, recess into which the positive electrode protrudes, and said recess is closed by a cap member which is provided with a short electrode extending into said recess and forming with the outer end of the positive electrode a spark gap whose sparks are easily visible through the trans parent walls of the recess.

This additional spark gap also has the function of intensifying the ignition spark.

Other novel features of construction and arrangement of parts will appear from the following description.

In the accompanying drawings, Fig. 1 is an elevation of my improved spark plug;

Fig. 2 is a longitudinal section of the same; Fig. 3 is a cross section along the line IIITII in Fig. 2, and Fig. 4; is an elevation of the insulator dismounted from the bushing but with the cap in place.

The following is a detailed description of the drawings.

A is a metal, preferably brass, bushing which is exteriorly threaded to be screwed into the hole in the cylinder head in the usual manner, and is provided with the negative PLUG.

Renewed Ecbruarv 1'7, 1922. Serial No. 537,356.

electrode 1. The upper bore of the bushing A is enlarged, forming an internal shoulder 2, and is threaded at its upper end.

B is the insulator made of heat resisting glass or some other suitable transsarent material. Intermediate of its ends tee insulator is provided with a circumferential flange 3 which, when the spark plug is assembled, fits down in the enlarged bore of the bushing and rests upon the shoulder 2, a gasket a being interposed to make a. gas-tight joint. The lower end of said insulator depends within the bushing A, as shown in 2, and is tapered to permit expansion of the material of the insulator. Above the flange 3 the insulator is provided with a cylindrical portion to lit the bore of the annular nut C which screws down into the threaded bore of the bushing A and bears against the flange 3 of the insulator B, a gasket 5 being interposed to give a gas-tight joint. Thus the insulator may be dismounted from the bushing by unscrewing the nut C.

Both the bushing A and the nut C are provided with hexagonal or other flattened perimeters for the application of a wrench or spanner, and the perimeter of the nut is sufliciently less than that of the bushing so that a spanner of the proper size to clutch the bushing will slip on the nut without catching, thus avoiding the danger of turning the nut in screwing up or unscrewing the bushing in the hole in the cylinder head.

The upper end of the insulator is tapered and preferably provided with longitudinal, exterior ribs, as shown, to prismatically facilitate the passage of light through the glass. The outer end of the insulator is pro vided with a circumferential lip 6. The outer end of the insulator is also provided with an axial recess 7, which is preferably tapered to assist in pressing the'insulator.

8 is the positive electrode, made of heat resisting wire such as a platinum alloy, embedded in the material of the insulator when the latter is pressed, and protruding from the lower end of the same to form a spark gap with the electrode 1. The insulator is pref rably countersunk or recessed, as at 9., thus permitting the material of the insulator to more safely expand. The upper end of the electrode 8 extends into the recess 7 and is provided with an enlarged or flattened 110 head 10 to give a more extended sparking terminal.

D is a metal, preferably brass, cap fitting on the outer end of the insulator B and closing the recess 7 to form a chamber. Said cap is provided with a depending annular flange 11 which fits down over the lip 6 of the insulator and is knurled under the same, as shown, to attach the cap permanently to the insulator, a copper gasket 12 being interposed between the outer end of the insulator and the cap to obtain a gas-tight joint. 7

13 is a Wire electrode fixed in the cap l) and extending into the recess 7 to a point adjacent to the end of the electrode 8, to "form a spark gap in the recess 7. he electrode 13 may be of nickel wire and should be o'l greater diameter than the electrode 8 and has a wider extended head 14, to increase the intensity of the spark and not to interfere with the delivery of full current to the ignition spark gap at the inner end of the spark plug. The outer end of the cap D is knobbed to receive the usual clip which forms the terminal of the circuit wire.

The cap D is or proper external diameter so that the nut C will slip freely down over the same, thus enabling me to first assemble the insulator and its cap, and then mount these assembled elements in the bushing. Thus the assembled insulator and cap may e supplied to users of my spark plug a repair part, ready to be mounted in the orig inal bushing after a broken insulator has been removed.

From the foregoing it is evident that sparking will occur in the air-tight chamber formed by closing the recess 7 with the cap D. thus indicating that the cylinder is firing and also the intensity of the spark obtained. By making the recess an air-tight chamber no impairment of current is involved by providing the secondary or visible spark gap.

The insulator with the positive electrode embedded therein is a very simple and inexpensive article to press irom molten glass, it being possible to make the same in large quantities and at a very slight cost in multiple molds. Where the visible spark gap chamber is formed in the interior of th' glass insulator, as in some types of snark plugs, the insulator must be mace in two parts, each part having a portion of the chamber formed in its end and having a part of the positive electrode embedded therein, and these parts are by a separate operation reheated and welded together. This of course is a very costly method of manufacture, but, aside from "that very important consideration, the heat required to weld the two glass parts together burns oil or fuses the protruding ends of the electrodes, thus impairing the character of the spark both at the visible spark gap and at the ignition spark gap. Also the welding clouds the walls of the chamber making the same more or less opaque and decreasin the visibility of the secondary sparking. (d ther visible spark plugs have been designed with porcelain insulators having transverse holes bored through them and the positive electrode gapped in the hole, the ends of the holes being covered either with glass or wire mesh. This is a very expensive construction and it is impossible to make the spark chamber 1 roperly air-tight.

ldy improved spark plug has an air-tight visible spark chamber, located at the upper end of the insulator where it is in full and easy view when the engine hood is raised, and the spark plug is also gas tight, as no can escape up along the positive electrode or between the bushing and the insulator. It is also free from becoming soaked with oil as do porcelain insulator spark plugs. Another advantage in using glass for the insulator material is that no matter what its temperature glass is always a nonconductor of electricity, while porcelain when suffieiently heated is no longer a nonconductor.

What I desire to claim is:

In a visible spark plug, the combination of a metallic bushing, a one-piece insulator integrally. pressed of vitreous transparent material and mounted in said bushing, the outer end of said insulator being provided with a concentric axial recess pressed in the end of said insulator to form a spark chamher, an electrode carried by said bushing, a second electrode embedded axially of said insulator and about which the molten material of said insulator is sealed in pressing the latter, one end of said axial electrode protruding from the inner end of said insulator to form with said first named electrode the ignition spark gap, while the other end of said axial electrode protrudes into said axial recess in the outer end of said insulator, said recess being of materially greater diameter than said axial electrode, a cap mounted on the outer endof said insulator and closing said recess to complete the spark gap chamber, and a third electrode extending through said cap into said chamber and forming a second spark gap with the outer end of said axial electrode.

Signed at Pittsburgh, Pa, this 5th day oi April, 1919.

FRANK A. HOWARD. 

